[107.15] The Microvariability of BL Lacertae During the 1997 Optical Outburst

We report optical R filter CCD photometric observations from
Colgate University's Foggy Bottom Observatory of the quasar
BL Lacertae during the intense outburst in summer 1997.
Throughout 1996 BL Lac hovered around a magnitude of R =
14.7-15.3, with night-to-night variations of several tenths
of a magnitude. The 1997 outburst appears to be part of a
general increase in activity which began after a minimum of
15.3 in July 1996. On June 23, 1997, BL Lac was observed to
be at its brightest in 20 years, after which we commenced
our intensive monitoring. BL Lac continued to be active
during the next two months, flaring numerous times during
this period within the range R = 14.2-12.4. Microvariability
was observed on several timescales. First, there are the
rises and declines, maxima and minima that occur over the
entire night (or longer) of amplitude a magnitude or
greater. A variability of 0.3-0.4 magnitudes over a six to
eight hour period is most common, but occasionally larger
changes occur. The maxima are very sharp, lasting only a
matter of minutes with slopes of up to 0.4 magnitudes per
hour near the peak, while the minima tend to be much more
gradual. Secondly, there is variability of 0.04-0.10
magnitude amplitude on timescales of minutes on top of this
night-long variation. The most common of these short-term
variations seem to be small flares that last 20 to 40
minutes.

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tbalonek@colgate.edu